Fertility clinics should send thousands of couples home without treatment, according to doctors whose research found that common frontline treatments often fail to improve a woman's chances of having a baby.

The study, reported in the British Medical Journal, showed that many women who were given the fertility pill clomifene, or who had intrauterine insemination (IUI), which involves injecting sperm directly into the womb, had no more babies than those who were sent home with nothing but advice on when best to have sex.

Siladitya Bhattacharya, a professor of gynaecology and obstetrics who led the study at Aberdeen University, said the treatments amounted to an enormous and unjustified cost to the NHS. He said the money spent could be redirected to improve the availability of IVF, which is considered to be more effective.

Nearly a third of couples who have trouble conceiving do not have any obvious medical problems, and in almost every case they are offered clomifene or IUI. Clomifene is effective in women who have stopped ovulating, but is given to others in the belief that it may boost their chances of conceiving. IUI is designed to overcome any problems sperm may have in passing through the cervix.

"A number of treatments have crept into fertility clinics over the years and are now part of our usual repertoire, but as with many things in infertility, most of these have not been properly evaluated," said Bhattacharya.

"Almost all couples with unexplained infertility will have one or both of these treatments, but neither of them is significantly more effective than telling the couple to just go home and get on with it, which is a lot cheaper and more fun," he added.

Last year doctors wrote more than 20,000 prescriptions for clomifene at a cost of more than £170,000. Fertility clinics charge between £500 and £1,000 for a single course of IUI.

In the study 508 women in their early 30s with unexplained infertility were randomly assigned to have either clomifene, IUI or no treatment at all. They were then monitored for six months and those who became pregnant were followed until they gave birth. Each had been trying to conceive for two-and-a-half years before joining the trial.

At the end of the trial 14% of women on clomifene had a live birth, compared with 24% who had IUI and 17% who were not given any treatment. But although there were differences in the figures, they were not large enough to be statistically significant, so cannot be attributed to the treatment itself.

"These treatments are offered by virtually every district hospital up and down the country, so the total costs are tremendous, particularly at a time when potentially more effective treatments such as IVF aren't being funded because of lack of money in the system," Bhattacharya said. "This has to change clinical guidelines because none of these interventions are free," he added.

In an accompanying editorial, Tarek El-Toukhy and Yacoub Khalaf from the Assisted Conception Unit at Guy's and St Thomas's NHS Foundation Trust, wrote: "As a direct result of the lack of evidence, many couples with unexplained infertility endure (and even request) expensive, potentially hazardous, and often unnecessary treatments."

Allan Pacey, an andrologist at Sheffield University and secretary of the British Fertility Society, said: "Intrauterine insemination has been offered to couples with unexplained infertility for many years, but if there is no benefit in doing so then we should re-evaluate the clinical guidelines so that NHS money is used wisely."